• Geomechanics and Engineering
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• 제16권1호
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• pp.35-47
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• 2018

This paper investigates the mechanisms of tunnel spalling and massive tunnel failures using fracture mechanics principles. The study starts with examining the fracture propagation due to tensile and shear failure mechanisms. It was found that, fundamentally, in rock masses with high compressive stresses, tensile fracture propagation is often a stable process which leads to a gradual failure. Shear fracture propagation tends to be an unstable process. Several real case observations of spalling failures and massive shear failures in boreholes, tunnels and underground roadways are shown in the paper. A number of numerical models were used to investigate the fracture mechanisms and extents in the roof/wall of a deep tunnel and in an underground coal mine roadway. The modelling was done using a unique fracture mechanics code FRACOD which simulates explicitly the fracture initiation and propagation process. The study has demonstrated that both tensile and shear fracturing may occur in the vicinity of an underground opening. Shallow spalling in the tunnel wall is believed to be caused by tensile fracturing from extensional strain although no tensile stress exists there. Massive large scale failure however is most likely to be caused by shear fracturing under high compressive stresses. The observation that tunnel spalling often starts when the hoop stress reaches $0.4^*UCS$ has been explained in this paper by using the extension strain criterion. At this uniaxial compressive stress level, the lateral extensional strain is equivalent to the critical strain under uniaxial tension. Scale effect on UCS commonly believed by many is unlikely the dominant factor in this phenomenon.

• 터널과지하공간
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• 제27권1호
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• pp.12-25
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• 2017

국내 석회석광산은 주로 자연통기에 의존하고 있으나 자본 및 운전비용이 과다하게 소요되는 광산 전체통기방법보다 풍관과 선풍기를 이용한 국부통기방법이 바람직한 방법으로 평가된다. 국내 대단면 장대 광산갱도에 풍관이 접속된 국부선풍기를 직렬로 연결 설치하는 경우에 통기시스템의 경제성과 효율의 최적화가 반드시 요구된다. 최적화를 위한 가장 중요한 두가지의 설계변수는 벽면 이격거리와 풍관 간의 이격거리이다. 본 연구에서는 경제적 및 환경적으로 최적화된, 즉 풍관간의 이격 공간을 통한 압력손실, 누기 그리고 오염된 공기의 재유입을 최소화할 수 있는 두 설계변수 값을 도출하기 위하여 광범위한 CFD분석을 시행하였다. 기존 연구결과와 권고기준들을 고려하여 이들 변수의 연구대상 범위를 선정하였다. 본 연구의 궁극적 목표는 국내 장대 광산갱도내 설치되는 풍관 접속 선풍기의 직렬연결 국부통기시스템의 최적화를 통하여 깨끗하고 안전한 작업장 환경을 제공하기 위함이다.

• 자원환경지질
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• 제3권4호
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• pp.199-222
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• 1970

One of the biggest sulfide metallic (Cu, Pb, Zn) ore deposits of South Korea is located in the area of Seo-myeon, Shiheung-gun, Gyeonggi-do. Geology of the region is mostly composed of metasediments of biotite schist, graphite schist, injection gneiss, sericite schist, limesilicate and quartzite from bottom, those are applicable to so-called Yeoncheon System of Pre-Cambrian, and granodiorite, quartz porphyry, basic dykes are outcroped in a small scope as intrusives. The origin of the ore deposit is pyrometasomatic contact deposits due to hydrothermal replacement and the ore bodies are imbedded in lower bed of limesilicate formation as impregnation and ore minerals are galena, sphalerite, marmatite, chalcopyrite, bornite, chalcocite, covellite, and the later two minerals are both hypogene and supergene. Gangue minerals are mostly skarn minerals those hornblende, diopside, epidote, hedenbergite, chlorite, garnet and quartz except primary calcite and quartz. Boundary plane (NS strike) between schists and limesilicate seemed to be primary opening of ore solution and fractures bearing $N50^{\circ}{\sim}80^{\circ}W$ are secondary structural control for localization of ore minerals and the third structural controls are both irregular gashes and schistosity in small scale. Photogeological study was carried with vertical aerial photo scaled 1: 38,000 and enlarged 1 : 10,000 under stereoscope. The study on the area convinced the fact that the geologic boundaries between rocks, limesilicates and quartzites, are traced easily by their typical topographic feature and drainage, and the main fracture patterns which derived from the result of fracture traces, that photogeologic lineament observed under stereoscope, are those bearing (1) $N20^{\circ}W$, (2) $N58^{\circ}W$, (3) $N76^{\circ}W$, (4) EW, (5) $N20^{\circ}W$, (6) $N62^{\circ}W$, (7) $N77^{\circ}W$. Among the written fractures, (5) (not schistosity, in case of fault) (6) (7) are post-mineral faults and others are pre-mineral faults and others are pre-mineral structures, and (2) (3) (6) (7) are coincided with statistical figure of 208 fractures surveyed in underground. By the result of the study, mineralized zone, are presumed to extend north and southward, total length about 4km.

• 터널과지하공간
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• 제14권1호
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• pp.43-53
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• 2004

본 연구에서는 지하 채굴적이 상부 지표 구조물의 안정성에 미치는 영향을 검토하기 위하여, 지하 채굴적의 심도와 보강 조건을 달리하는 네 가지의 경우에 대해 축소모형실험을 실시하였다. 이를 위해 실험목적에 부합한 모형 실험장치를 제작하였으며, 모형재료는 석고, 모래, 물의 혼합물을 사용하였다. 채굴적의 심도가 깊은 모형의 균열 개시압력은 얕은 모형에 비해 2.5배 더 크게 나타나 채굴적이 깊을수록 지반의 안정성은 우수하였다. 구조물의 하부 지반을 그라우팅으로 보강한 모형은 무보강 모형에 비해 균열 개시압력이 2.4배 커져, 보강을 실시하면 지반 안정성이 증가하는 것으로 나타났다. 또한, 대규모 보강을 실시한 경우는 소규모 보강에 비하여 최대 침하량이 작을 뿐 아니라 침하곡선이 완만하여 경사와 곡률도 작아지므로 지반 안정성은 보다 더 커질 것으로 판단된다.